(O–C) of the reconstructed colors for dwarf stars. We plot the difference between colors obtained from our “spectral type – luminosity class – color” relationships and from photometric measurement. Each circle corresponds to a star in the Ducati (2002) catalogs and with a know spectral type. The rms of the (O−C) are computed in three ranges of spectral type. We emphasize that the interstellar reddening is not corrected in the Ducati (2002) catalog, this is certainly the more important source of scattering for OB stars and M-giants (statistically more distant stars and therefore more subject to reddening).